typedef struct _DEVICE_OBJECT
{
     SHORT Type;
     WORD Size;
     LONG ReferenceCount;
     PDRIVER_OBJECT DriverObject;
     PDEVICE_OBJECT NextDevice;
     PDEVICE_OBJECT AttachedDevice;
     PIRP CurrentIrp;
     PIO_TIMER Timer;
     ULONG Flags;
     ULONG Characteristics;
     PVPB Vpb;
     PVOID DeviceExtension;
     ULONG DeviceType;
     CHAR StackSize;
     BYTE Queue[40];
     ULONG AlignmentRequirement;
     KDEVICE_QUEUE DeviceQueue;
     KDPC Dpc;
     ULONG ActiveThreadCount;
     PVOID SecurityDescriptor;
     KEVENT DeviceLock;
     WORD SectorSize;
     WORD Spare1;
     PDEVOBJ_EXTENSION DeviceObjectExtension;
     PVOID Reserved;
} DEVICE_OBJECT, *PDEVICE_OBJECT;

Windows Vista Kernel Structures